1. Field of the Invention
The present invention relates to a an ink jet printing system and method using a print head including nozzle arrays for respective different types of ink and in which the print head performs a plurality of scans to print an image in a predetermined area on a print medium, as well as a relevant storage medium.
2. Description of the Related Art
A multi-pass printing scheme is a printing scheme for ink jet printing apparatuses; in the multi-pass printing scheme, an image is printed in a stepwise fashion by a plurality of print scans of the same print area on a print medium. In the multi-pass printing scheme, an image is printed while repeating a print scan in which ink is ejected from a print head being moved in a main scanning direction and a conveying operation of conveying the print medium in a sub-scanning direction by 1/N of a print width for a single print scan. In the multi-pass printing, the print medium is conveyed between the current print scan and the next print scan. Thus, the print head provides ink droplets to the same print area on the print medium at predetermined time intervals. Thus, for print media such as plain paper which slowly absorbs pigment ink, printing can be performed while ink droplets applied to the print media are being dried. As a result, the ink can be appropriately fixed to the print media.
However, when multi-pass printing is performed on print media such as glossy paper the surface of which is specially processed, the glossiness of an image print portion may be impaired.
In general, fine pores are formed in the surface of print media such as glossy paper to improve absorption of an ink solvent and fixation of a color material. For dye ink, the dye is absorbed via the pores together with moisture. However, for pigment ink, pigment molecules are difficult to dissolve into water and disperse in the moisture in the form of particulates. Each of the particulates is larger than the pore. Thus, the color material is difficult to permeate to the interior of the print medium. That is, it is expected that the pigment particulates are fixed to the surface of the print medium in such a way as to be accumulated, thus impairing the smoothness of the surface to make the surface non-glossy.
Moreover, in the multi-pass printing, if pigment ink is used which contains a color material difficult to permeate to the interior of the print medium, the ink applied during each print scan dries sequentially on the print medium and is overlappingly fixed. For example, in multi-pass printing (four-pass printing) in which an image is completed by scanning the same print area on the print medium four times, four layers of ink are laid on top of one another. In contrast, in single-pass printing (one-pass printing) in which an image is completed by scanning the same print area on the print medium once, one ink layer is formed. Thus, the multi-pass printing provides the surface of the print medium with larger irregularities and is more likely to make the surface non-glossy than the single-pass printing.
As is well known, the ink jet printing scheme has the following characteristics. If ink droplets applied to the print medium during the same scan (same pass) come into contact with one another on the print medium surface before the fixation is completed, leveling occurs to reduce the irregularities of the print medium surface to improve the gloss of the surface.
Japanese Patent Laid-Open Nos. 2005-297212 and 2008-162095 disclose techniques of varying the probability of the contact between two ink droplets to control the level of leveling to achieve preferable gloss. That is, the technique in Japanese Patent Laid-Open No. 2005-297212 is used for an ink jet printing apparatus using pigment ink, to allow the number of passes or a mask pattern to be selected in accordance with the glossiness of the print medium. This allows a change in the number of passes and thus in the print ratio for the same pass. Furthermore, according to the technique in Japanese Patent Laid-Open No. 2008-162095, the mask pattern is selected in accordance with the glossiness of the print medium to change the continuity of ink dots formed during the same pass. This makes ink droplets likely to come into contact with one another during the same pass for each of plural types of ink. These techniques enable the appropriate glossiness of the glossy print medium to be maintained with degradation of glossiness of the image print portion minimized.
However, if the method disclosed in Japanese Patent Laid-Open No. 2008-162095 is used to perform printing such that ink droplets come into contact with one another on the print medium for each of plural types of ink, dots of each type of ink are excessively large. Thus, particularly colors with low lightness become noticeable to degrade the granularity of images. On the other hand, according to the method disclosed in Japanese Patent Laid-Open No. 2005-297212, a reduction in the number of passes may lead to beading in which ink droplets stick to one another, causing the stuck ink droplets to be localized. This may degrade the granularity.
Furthermore, if ink droplets previously formed on the print medium hinder permeation of subsequently applied ink droplets (subsequent ink droplets), the subsequent ink may concentrate and aggregate in an uncolored area on the print medium in which ink dots have not been formed yet. In this case, the subsequent ink with a high color material concentration becomes massive during the aggregation. This makes the irregularities on the surface of the print medium larger to allow light to scatter more wildly. As a result, the gloss of the surface may be degraded. Moreover, since ink with a high color material concentration and a low lightness is more noticeable, localization and aggregation of such ink may degrade the granularity of images.
As described above, the conventional printing methods have difficulty suppressing degradation of the gloss resulting from the irregularities on the surface of the print medium and degradation of granularity of images at the same time. In particular, if a high density image is printed, as ink with a high color material concentration is used for printing, the irregularities on the surface of the print medium are likely to be larger, resulting in a reduction in the glossiness of the surface.